The use of electrical stimulation of the spinal cord or associated nerve bundles for the reduction of bodily pain is well known in the art of pain relief. Leads containing electrodes are commonly used for such electrical stimulation and are implanted on or near a nerve bundle or the spinal cord. A pulse generator that supplies electrical pulses with predetermined characteristics is typically connected to the lead.
In a typical embodiment of the prior art, a stimulating lead incorporating multiple electrodes is constructed in a cylindrical, elongated and flexible lead configuration. The lead is then inserted into the spinal canal's epidural space and adjacent to the posterior aspect of the spinal cord. Alternatively, a lead may be inserted into the body next to or alongside the desired peripheral nerve.
A pulse generator transmits electrical pulses through two or more connecting wires within the lead to the electrodes, which by its proximity to the desired stimulation site, stimulates a certain area of the spinal cord or the peripheral nerve. In the case of spinal cord stimulation, the electrical pulse at the electrodes can negate the passage of pain sensation from peripheral areas such as a leg or arm, to the brain.
In the case of a lead inserted to lie alongside a peripheral nerve, stimulation of the nerve induces depolarization of the nerve and propagation of a nerve impulse towards the spinal cord. This also appears to negate unpleasant sensations conducted in the nerve. Various peripheral nerves have been stimulated by this latter technique including peripheral nerves to the limbs and to the cranium.
Multiple configurations of products and nerve stimulation currently exist. Papers by Holsheimer entitled “Effect of anode-cathode configuration on paresthesia coverage in spinal cord stimulation” and Hassenbusch, et. al. entitled “Long-term results of peripheral nerve stimulation for Reflex Sympathetic Dystrophy” describe various aspects of nerve stimulation and are incorporated by reference here in full.
Power to and control of such stimulating electrodes is derived from either fully implantable battery powered devices or generators, or alternatively, from radiofrequency systems, where the power is transmitted through the skin by closely applied transmitting coils. The Genesis® and Renew® systems, provided by Advanced Neuromodulation Systems, Inc. are two similar systems existing in the prior art that utilize this methodology. Such systems are further described in more detail in U.S. Pat. No. 4,793,353, which is incorporated by reference here in full.
Various configurations of leads have been designed and typically involve multiple electrodes of 2-3 mm in size, in multiples of 4 or 8. Such electrode arrays are inserted through an introducing needle into the epidural space, or in the case of a peripheral nerve are placed adjacent to the nerve either through a hollow needle or by open surgery. The power source and the electrode array are typically connected by a subcutaneous borrowed connector, which passes around the body to a suitable location such as the groin or lateral chest wall.
These products have been developed for treatment of chronic pain often where nerves have been injured or involved in surgery. Electrical stimulation provides a safe and minimally invasive means of controlling chronic pain without resorting to drugs.
The current treatment of discogenic (i.e., originating in the intervertebral disc) spinal pain is not satisfactory. Patients can be offered conservative management including physiotherapy treatment, medication and psychological techniques such as cognitive behavioral therapy. Presently, techniques exist of heating the annulus fibrosus using radiofrequency annuloplasty for painful annular tears causing discogenic low back pain.
This procedure is available for a relatively small group with only moderately degenerated discs. For a much larger group of patients with more advanced degeneration of the disc, often at multiple levels of the spine, presently, there is only surgery in the form of spinal fusion that can be offered.
Certain studies show that the results of spinal fusion are not ideal. For example, in the lumbar region only approximately 63% of patients improved, and approximately 30% experienced no improvement at all, or in some cases, worsening of the pain state.
Once a major operation such as a spinal fusion has been conducted, the anatomy of the spine is permanently changed. Secondary problems can also occur with altered mechanics of the spine, changes in nerve function and increased pressure on the discs at other spinal levels, which may need further surgery.